250w vs 400w HPS in 3x3 heat output (winter grow, autoflowers)

Hey guys, i know this is probably an over-asked question but i don't seem to find an answer to my question.. im about to start my first grow and my budget is limited but its much cheaper to grow my own than purchasing it every week.. So basically i want to grow 4 plants (Northern Lights autoflowers inside 11L pots) inside a 80x80x160cm tent which is going to be placed inside a room 5x5m.
So, i thought about putting them under a 250w HPS light, and the exhaust would be a carbon filter> 4 inch fan>ducting into room with no bends.
But then i thought if i could maybe put a 400w HPS instead of 250w to get better yield and i would put an oscillating fan to blow directly on the light to cool it down. So now i dont know if the 4 inch fan is going to be able to pull all of the hot air outside the tent to keep the tems down around 27-30c inside but since we have cold weather here until late march i thought its going to work until then (upgrading later). Sorry for long read i would much appreciate your answers.

Is your exhaust pumping into the same room the tent is in?

Yes. I would open the windows to let fresh cold air in when needed

If your exhausting directly into the room where your tent is, you will heat up the room over time and end up cooking your entire grow. Best option would be to run the exhaust to the exterior window and exhaust outside. That way all the heat is exhausted out of your room.

If you need to exhaust into your room and cant take the exhaust outside, I have found that 200W of LED light is the limit to not overheat a room.

If you were to just open the windows as needed to bring the heat down. you will be creating hot and cold swings in your room, and you will need to remember to get the window shortly after lights on every day to keep your temps in check.

That being said, I personally have run a 600W HPS in a 3'x3' tent with no issues using a 4" fan and exhausting to the exterior. The ambient room temperature was 70F and i was able to keep the tent temperatures in the 80-85F range.

Alright thanks for your answer. I don't have an option to exhaust the hot air directly outside right now. I'll keep that in mind later when i will upgrade my tent. I guess i will stick with 250w HPS and opening windows this winter.
So my next question now is 250w light good enough for 4 plants in 11L pots (Northern lights auto) or should i just stick with three. How much dry yield can i expect?

I ran a 400 in a 30x30,vented with 4" into my veg room.Then vented out side.Tent was in a cool room 63-66f.Worked fine but i only had one plant.

I had leds in my veg room so my 400hps kept my room a little warmer.With your window open a little youll be fine.Winter is hps time.lol

The enclosed glass hoods with the exhaust fan hooked right up to them reall sucks the heat away from the bulb aswell.



Or the cool tubes



A good buy is to purchase a 600W digital HID hps/mh light kit with hood / ballast/ bulbs,there dirt cheap as a complete kit under $150, the digital ballasts are capable of dimming to 300 or 450 watts, or the full 600 if you can exhaust the heat. The enclosed hoods really help not scorch the plants and you can get them quite close to the glass if they peak a little higher than you have room for